Tub grinders are widely used in agriculture to grind roughages and grains. Most prior tub grinders have a stationary floor member about which a cylindrical tub member is rotated. The material is moved over the upper surface of the stationary floor member and into the path of a rotating hammermill or other grinding apparatus. A portion of the rotating hammermill extends above the upper surface of the stationary floor member through an opening therein and the material is fed into the hammermill in a direction substantially perpendicular to the axis of rotation of the hammermill. Examples of such prior tub grinders include U.S. Pat. No. 4,003,502 to Barcell issued on Jan. 18, 1977, and U.S. Pat. No. 2,650,745 to Oberwortman issued on Sept. 1, 1953. In U.S. Pat. No. 3,615,059 to Moeller issued on Oct. 26, 1971, the tub member 12 is oscillated about an axis to advance the material toward the opening 44. U.S. Pat. No. 3,483,906 to Moeller issued on Dec. 16, 1969, also oscillates the tub member 16 relative to the floor member to advance the material. In this patent, a cover member 58 is provided in FIG. 4 which can be used as a valve to adjust the size of the opening 62 above the grinder 28. Other grinders and apparatuses in this general field include U.S. Pat. No. 3,550,661 to Moeller issued on Dec. 29, 1970, U.S. Pat. No. 3,861,601 to Kaelin issued on Jan. 21, 1975, U.S. Pat. No. 3,556,605 to Berg issued on Jan. 19, 1971, and U.S. Pat. No. 2,839,250 to Brockman issued on June 17, 1958.
All known prior art tub grinders have major problems in delivering material from the floor member downwardly into the grinder at a uniform rate. They also have serious problems with material falling down into the casing of the grinder or coming to rest on top of the grinder elements when the tub grinder is shut down or slowed down by a power governor. The material falling into the casing by gravity or resting atop the grinding elements makes it extremely difficult to restart the tub grinder or bring the rotating grinder back up to peak speed after a slowdown. The problems of uniform feed and material clogging the casing during a shutdown or slowdown are particularly acute if the material is wet.
Past tub grinders have further problems with versatility in that they cannot be easily and quickly adapted to handle different materials and material in different degrees of compactness as for example from bales to loose stack and from wet to dry. The grinding apparatus or hammermill of prior tub grinders also lack versatility in that they cannot be easily and quickly adapted to adjust the grind size of the ground material for any given material or for a different material that may be placed in the tub grinder. Control of the amount of air and material leaving the casing after being ground has also been a problem area in past tub grinders.
The ideal tub grinder would be durable, simple in design, able to uniformly feed material into the grinder, versatile, and easy to restart after being shut down or slowed down by a power governor. For versatility, the ideal tub grinder would be easily and quickly adaptable to handle a wide variety of materials in various degrees of compactness and wetness as well as easily and quickly adaptable to adjust the grind size of the material. The present invention offers such a tub grinder.